German Patent Application No. DE 199 06 287 describes a method for controlling an internal combustion engine, in whose exhaust-gas region an exhaust-gas treatment device is situated that includes a particulate filter which holds back the particulates contained in the exhaust gas. For proper operation of the particulate filter, it is necessary to know the particulate load state, which may be determined indirectly based on the differential pressure occurring at the particulate filter.
A particulate filter is regenerated by a burn-off of the particulates embedded in the particulate filter, which takes place in a temperature range of 500° C.-650° C., for example.
German Patent Application No. DE 199 06 287 describes a method for controlling an internal combustion engine, in whose exhaust-gas region a particulate filter is situated. When the load state of the particulate filter exceeds a predefined quantity, a regeneration of the particulate filter is initiated. In particular, it is provided that fuel should additionally reach the exhaust-gas region of the internal combustion engine, the fuel reacting exothermically as combustible material in the exhaust-gas region. For example, the fuel is oxidized on the catalytically active surface of a catalytic converter. This raises the temperature of the catalytic converter, on one hand, and on the other hand, the temperature of the exhaust-gas flow which appears downstream of the catalytic converter and acts upon the subsequent particulate filter. For example, by adjusting the start of injection of the fuel fed to the internal combustion engine, the combustible material gets into the exhaust-gas region and does not already burn in the cylinder.
German Patent Application No. DE 100 56 016 describes a method for operating a particulate filter, in which fuel is likewise introduced into the exhaust-gas region of the internal combustion engine and reacts exothermically for heating the particulate filter in the exhaust-gas region. The fuel is introduced by at least one non-burning secondary fuel injection, which can be influenced by the point of time specific to the crankshaft angle, the duration of the fuel injection and the fuel pressure. The duration and the pressure yield the quantity of combustible material per secondary injection.
Depending on the operating conditions in the combustion chambers of the individual cylinders of the internal combustion engine, the non-burning fuel partially condenses on the cylinder walls and gets past the piston rings into the crankcase. Therefore, the secondary injections of fuel can contribute to the oil dilution.
German Patent Application No. DE 196 02 599 describes a method for determining a quantity of oil in an internal combustion engine, in which the oil level is measured by an oil sensor. The method makes it possible to ascertain the oil level comparatively accurately during operation of a motor vehicle.
An object of the present invention is to provide a method for operating an internal combustion engine in which at least one secondary injection of fuel is carried out, and a device for implementing the method, which permit reliable operation of the internal combustion engine.